As mobile devices have been increasingly developed, and the demand for such mobile devices has increased, the demand for secondary batteries has also sharply increased as an energy source for the mobile devices. Among them is a lithium secondary battery having high energy density and high discharge voltage, on which much research has been carried out and which is now commercially and widely used.
Based on the appearance thereof, the lithium secondary battery may be classified as a cylindrical battery, a prismatic battery, or a pouch-shaped battery. A recent trend in the miniaturization of mobile devices is increased demand for prismatic batteries or pouch-shaped batteries, which have a small thickness. Especially, the pouch-shaped battery has attracted considerable attention because the form of the battery can be easily changed, the manufacturing costs of the battery are low, and the weight of the battery is small.
Generally, the pouch-shaped secondary battery is constructed in a structure in which an electrode assembly including cathodes, anodes, and separators disposed respectively between the cathodes and the anodes is mounted in a pouch-shaped battery case in a sealed state while two electrode leads, which are electrically connected to cathode and anode taps extending from the electrode assembly, are partially exposed to the outside of the battery case at one end of the battery case.
However, the pouch-shaped battery is constructed in a structure in which the battery case, having a thickness of approximately 113 μm, includes an outer coating layer made of oriented nylon film (ONy), a barrier layer made aluminum, and an inner sealant layer made of cast polypropylene (CPP). As a result, the pouch-shaped battery may be easily damaged when physical impacts are applied to the pouch-shaped battery or a pointed object presses the pouch-shaped battery, and therefore, the pouch-shaped battery may catch fire or explode. In order to solve this problem, therefore, there are technologies being generally used for increasing the thickness of the battery case or using an additional member, such as an outer case made of a material having high mechanical strength. However, the increase of the thickness of the battery case or the use of the additional member increases the volume of the pouch-shaped battery and complicates a process for manufacturing the pouch-shaped battery.
Consequently, the present invention provides a technology for deforming sealing parts of a battery case to improve the safety of the battery case against impacts applied to the battery case without increasing the volume of a battery and affecting the process for manufacturing the battery.
In this connection, Japanese Patent Application Publication No. 2005-116278 discloses a technology for winding sealing parts of a battery case in the direction where an electrode assembly receiving part of the battery case is positioned such that the sealing parts of the battery case is brought into tight contact with the electrode assembly receiving part of the battery case. This technology is to prevent the leakage of an electrolyte from the battery case. However, this technology has a problem in that the battery case between the winded sealing parts and the electrode assembly receiving part may be weakened and thus damaged.
Also, Japanese Patent Registration No. 3527858 discloses a technology for bending sealing parts formed along the edge of an electrode assembly receiving part of a battery case and bending ends of the respective sealing parts by plastic deformation. In the disclosed technology, electrode terminals protrude in the same direction at one end of the battery case. However, this technology has a problem in that it is difficult to connect the electrode terminals to corresponding electrode taps, and a short circuit may occur when external forces are applied to the battery case. Furthermore, since the sealing parts are bent and deformed by plastic deformation, the sealing parts, which are made of a laminate sheet and formed by thermal welding, may be excessively deformed with the result that the mechanical strength and the coupling force of the sealing parts may be reduced, and the manufacturing process is complicated.